1. Field of the Invention
The present invention relates to a fundus capturing apparatus.
2. Description of the Related Art
A split prism for observation in a fundus capturing apparatus (also referred to as “fundus camera” in the following) moves in an optical-axis direction in cooperation with the adjustment of a focus lens, and needs to perform an advancing and retracting movement, in which it enters the optical axis during observation and leaves the optical axis during capture. The configuration disclosed in Japanese Patent Laid-Open No. 2009-247772 is common, and this configuration example is explained with reference to FIG. 4.
A split prism driving mechanism 40 includes a split prism 401, a split base 402, a split shaft 403, a split advance/retract driving mechanism 404, a split advance/retract driving motor 405, a split shift base 406, a split shift shaft 407, a split shift anti-vibration shaft 408, and a split shift driving mechanism 409.
The split base 402, which holds the split prism 401, is fitted to the split shaft 403 such that it is rotatable with respect to the split shaft 403. When the split advance/retract driving motor 405 is operated, the split advance/retract driving mechanism 404 rotates the split base 402 with respect to the split shaft 403, and the split base 402 is retracted from the illumination optical axis. These components constituting a split advancing/retracting mechanism are fixed to the split shift base 406.
Moreover, when the split shift base 406 is driven by the split shift driving mechanism 409, the entire split advancing/retracting mechanism is moved along the split shift shaft 407 in the illumination optical-axis direction. It should be noted that at that time, it is moved in the illumination optical-axis direction while its rotation is limited by the split shift anti-vibration shaft 408.
It is uncertain where in the operation range the split shift operation stops, and it is necessary to perform an advancing/retracting operation from the location where it has stopped. Consequently, since the split advancing/retracting movement and the split shift movement need to be performed independently, a configuration is adopted, in which the entire split advancing/retracting mechanism is subjected to split shift movement.
However, in this conventional mechanism in which the entire split advancing/retracting mechanism is subjected to split-shifting, there is the problem that it is difficult to determine the split position with high precision.
The present invention provides a technique for determining the split position with high precision.